The present invention relates to a heat accumulator, and particularly for latent heat.
More particularly, it relates to a heat accumulator which has an inner casing having an accumulator core with a storage medium, and an outer casing surrounding the inner casing at a distance thereto to form an insulation space therebetween. The present invention also deals with a method of manufacture of the heat accumulator.
In a heat accumulator known from DE-40 20 859 A1 the insulation space formed between the inner casing and outer casing is baked out and evacuated to remove gases. Evacuation is effected in order to achieve the best possible insulation by keeping losses as low as possible in the heat accumulator. It is known that substances such as H.sub.2 O, H.sub.2 or the like evolving under vacuum from the walls forming the boundary of the insulation space retard the evacuation process. For this reason, the insulation space is baked out so that these substances can be sucked out more quickly. Baking out is effected after the housing of the heat accumulator has been completed and the storage medium has been introduced into the accumulator core. A reasonable baking out temperature for the insulation space often lies above the maximum permissible temperature of the storage medium so that there is a risk of damaging the storage medium by excessive temperatures. Therefore, steps are taken in a heat accumulator to insulate the accumulator core from the insulation space by protective devices during bake-out and accordingly to prevent overheating of the storage medium. Such protective devices are costly. Cooling measures for protecting the storage medium against damage during baking out are likewise costly.
Further, a heat accumulator is known (FR-26 67 934, A1) in which the insulation space is baked out before introducing the storage medium and the storage medium is introduced only after the baking out process. The risk of damage to the storage medium is avoided in this way and protective devices, e.g., for cooling the storage medium or protecting it from excessive temperatures during baking out, can be dispensed with. Further, a higher temperature can be selected for baking out the insulation space. In this known heat accumulator, the pipe connection having a fill opening through which the inner casing is filled with the storage medium extends from the inner casing through the insulation space and outer casing to the outside. The external fill opening of the pipe connection can be closed by a closing element. Further, an alternative solution in this heat accumulator consists in that the pipe connection of the inner casing whose fill opening is closed by a closing element is located in the interior of a feed line or outlet line through which the operating medium can be fed to or removed from the accumulator core during operation of the heat accumulator. In this construction, the only access to the fill opening of the inner casing is through the feed line or outlet line and is accordingly difficult. The other construction in which the pipe connection proceeds from the inner casing and passes through the insulation space and outer casing involves drawbacks for the manufacture of the heat accumulator. For example, insertion of the accumulator core in the outer casing becomes difficult. A further disadvantage in the known heat accumulator consists in that it is sometimes difficult to introduce the storage medium into the accumulator core. Special steps for introducing the insulating medium in the insulation space are not provided in the known heat accumulator.